US Patent RE43431: Scope, Claims, Expiration and Patent Landscape for Neratinib
US Patent RE43,431 is a reissue patent covering quinazoline-based irreversible ErbB receptor tyrosine-kinase inhibitors, including neratinib and defined stereoisomers and acid-addition salts. The commercial compound most directly implicated by the claims is neratinib, marketed in the United States as Nerlynx by Puma Biotechnology. The patent is important for composition-of-matter coverage, but its practical exclusionary value must be assessed against the original patent term, later Nerlynx patents, FDA Orange Book listings, and any patent-term adjustment or pediatric extension.
What drug does US RE43431 cover?
US RE43,431 covers neratinib and a genus of structurally related 4-anilinoquinazoline compounds.
Neratinib is the compound identified in claim 8:
4-[(3-chloro-4-fluorophenyl)amino]-6-{[4-(N,N-dimethylamino)-1-oxo-2-buten-1-yl]amino}-7-((S)-(tetrahydrofuran-3-yl)oxy)quinazoline.
The compound is also known as:
- Neratinib
- Neratinib maleate
- HKI-272
- PB272
- Nerlynx
Neratinib is an irreversible inhibitor of HER2, EGFR, and HER4. FDA approved Nerlynx in 2017 for extended adjuvant treatment of early-stage HER2-positive breast cancer following adjuvant trastuzumab therapy. FDA later expanded the indication to include certain patients with advanced or metastatic HER2-positive breast cancer in combination with capecitabine. [1]
What is the chemical scope of RE43431?
The independent chemical claim covers a substituted quinazoline core with three principal variable regions:
| Structural position |
Claimed substituent category |
| Anilino substituent, Ra |
Benzyl, 1-phenylethyl, or 3-chloro-4-fluorophenyl |
| Aminobutenoyl substituent, Rb |
Dimethylamino and specified secondary or cyclic amino groups |
| Oxygen substituent, Rc |
Cycloalkoxy, tetrahydrofuranyloxy, tetrahydrofuranylmethoxy, tetrahydropyranyloxy, or tetrahydropyranylmethoxy |
The claim architecture narrows through dependent claims:
- Claim 1 establishes the principal Markush genus.
- Claim 2 narrows Rb to dimethylamino.
- Claim 3 removes the benzyl option for Ra and retains 1-phenylethyl or 3-chloro-4-fluorophenyl.
- Claim 4 again narrows Rb to dimethylamino.
- Claim 5 specifies the 3-chloro-4-fluorophenyl and dimethylamino combination.
- Claim 6 specifies the 3-chloro-4-fluorophenyl, dimethylamino combination with selected oxygen substituents.
- Claim 7 narrows Rc to tetrahydrofuran-3-yloxy.
- Claim 8 claims the specific S-enantiomer corresponding to neratinib.
- Claims 9 to 11 cover physiologically acceptable acid-addition salts, including neratinib maleate.
- Claim 12 separately claims the R-enantiomer.
The patent therefore combines broad genus protection with progressively narrower species claims. Claims 8 and 11 are commercially significant because they identify the active pharmaceutical ingredient and the maleate salt used in Nerlynx.
Which claims most directly cover neratinib?
Claims 8 and 11 provide the clearest direct coverage of commercial neratinib.
| Claim |
Commercial relevance |
| Claim 5 |
Covers the key 3-chloro-4-fluorophenyl and dimethylamino substitution pattern but leaves Rc broader |
| Claim 6 |
Narrows the structure to the commercial aniline and dimethylamino combination with selected oxygen substituents |
| Claim 7 |
Covers the tetrahydrofuran-3-yloxy substitution pattern |
| Claim 8 |
Specifically claims the S-enantiomer of neratinib |
| Claim 9 |
Covers physiologically acceptable salts of claim 8 |
| Claim 10 |
Lists acceptable inorganic and organic acids |
| Claim 11 |
Specifically covers the maleate salt |
| Claim 12 |
Covers the R-enantiomer |
The most commercially valuable claim is claim 11 because Nerlynx is supplied as neratinib maleate. Claim 8 independently protects the active S-enantiomer even without limiting the salt counterion.
How broad is the composition-of-matter coverage?
The claims are materially broader than neratinib alone. They cover a family of quinazoline compounds differentiated by:
- Aromatic aniline or phenethyl groups;
- Multiple dimethylamino and substituted amino side chains;
- Saturated cyclic ether substituents;
- Both R and S stereoisomers;
- Free bases and pharmaceutically acceptable salts.
The claim set is narrower than an unrestricted quinazoline genus because each variable is limited to a closed list of named substituents. A compound would generally need to satisfy every limitation of at least one claim. A structurally related kinase inhibitor with a different aniline substituent, different amino side chain, or different cyclic ether may fall outside the literal wording, although doctrine-of-equivalents arguments could remain relevant in litigation.
The claims do not expressly cover every formulation, dosage regimen, manufacturing process, or method of treating cancer. Their primary value is product protection.
What is the scope of claim 1?
Claim 1 is a Markush composition claim. It requires a compound of formula I with all three substituent classes selected from the listed groups.
Its practical scope includes compounds having:
- A permitted Ra group;
- A permitted Rb amino group; and
- A permitted Rc alkoxy or ether-containing group.
The use of “or a stereoisomer or physiologically acceptable salt thereof” extends claim 1 beyond a single neutral molecular form. It captures stereochemical variants and salt forms, subject to the underlying structure satisfying the formula.
Claim 1 is potentially vulnerable to prior-art attacks if an earlier reference discloses the same combination of substituent classes or makes the claimed genus sufficiently predictable. Claims 8 and 11 are narrower and generally easier to analyze for anticipation, but their commercial importance can make them more valuable in enforcement.
What is the scope of the neratinib maleate claim?
Claim 11 covers the maleic-acid salt of the claim 8 S-enantiomer. This corresponds to neratinib maleate, the active ingredient in Nerlynx.
The claim is narrower than a claim to all neratinib salts, but it is commercially important because:
- The maleate salt is the marketed drug form.
- A generic applicant seeking to market the same salt would face direct product-claim exposure.
- A different salt could avoid literal infringement of claim 11, but could remain subject to claims 8 or 9 depending on the product form.
- Solid-state, polymorph, particle-size, formulation, or process patents may create separate barriers even if a challenger avoids RE43,431.
When does RE43431 lose exclusivity?
RE43,431 is a reissue patent. A reissue does not ordinarily create a new patent term. Its term is tied to the original patent from which it was reissued. The relevant expiration analysis therefore requires review of the original patent, any patent-term adjustment, terminal disclaimer, patent-term extension, and pediatric exclusivity.
Public patent records identify RE43,431 as a reissue of the earlier neratinib patent estate. The reissue itself should not be treated as having a fresh 20-year term beginning on its 2013 issue date. The commercially relevant expiration date is the expiration date carried forward from the original patent, subject to statutory adjustments. [2]
The principal term implications are:
| Issue |
Effect |
| Reissue filing or issue |
Does not restart the patent term |
| Original nonprovisional filing date |
Controls the basic 20-year term |
| Patent-term adjustment |
Can extend the expiration date |
| Patent-term extension under 35 U.S.C. §156 |
Could extend an approved product patent if granted |
| Pediatric exclusivity |
Adds six months to eligible listed patent or exclusivity periods |
| Later continuation patents |
May expire later and create separate barriers |
A reliable freedom-to-operate conclusion cannot be based on the reissue issue date alone. The original patent record and current FDA listing must be consulted together.
What is the FDA Orange Book status of neratinib?
Neratinib maleate is an FDA-approved small-molecule drug and is eligible for Orange Book patent listing. Orange Book-listed patents are evaluated separately from the broader historical RE43,431 patent family.
The FDA Orange Book may include patents directed to:
- The active ingredient;
- The salt or solid form;
- Pharmaceutical compositions;
- Methods of use;
- Dosing regimens;
- Treatment of HER2-positive breast cancer;
- Combination treatment with capecitabine.
The presence of RE43,431 in the historical patent estate does not establish that it remains an active Orange Book barrier. A current generic applicant would evaluate the specific patents listed for the relevant Nerlynx reference product and the certifications required under the Hatch-Waxman Act. [3]
How does a Paragraph IV challenge affect RE43431?
A generic applicant filing an abbreviated new drug application may submit a Paragraph IV certification alleging that an Orange Book-listed patent is invalid, unenforceable, or not infringed.
For RE43,431, the principal Paragraph IV theories would likely involve:
- Anticipation of the claimed neratinib structure;
- Obviousness based on earlier 4-anilinoquinazoline kinase inhibitors;
- Written-description or enablement challenges to the Markush genus;
- Lack of support for the claimed stereochemical forms;
- Noninfringement based on a different salt, polymorph, or active form;
- Patent-term or listing challenges.
A Paragraph IV notice can trigger patent litigation under 21 U.S.C. §355(j), generally creating a 30-month stay of FDA approval if the NDA holder or patent owner files suit within the statutory period. [4]
A generic developer can also use a section viii “carve-out” for a patented method of use if the proposed label excludes the protected indication. That strategy is less useful against a composition claim covering the active ingredient or marketed salt.
Which patents compete with RE43431 in the Nerlynx estate?
The Nerlynx estate includes more than one patent family. The relevant categories are:
| Patent category |
Typical commercial function |
| Core composition patents |
Protect neratinib and related quinazoline compounds |
| Salt patents |
Protect neratinib maleate or other pharmaceutically acceptable salts |
| Solid-state patents |
Protect polymorphs, crystallinity, or physical form |
| Formulation patents |
Protect tablets, excipients, dissolution, or stability |
| Method-of-use patents |
Protect extended adjuvant and metastatic breast-cancer use |
| Manufacturing patents |
Protect intermediates, stereochemical resolution, or synthesis |
| Dose and regimen patents |
Protect low-dose schedules or combination treatment |
Core composition patents generally present the strongest barrier because they cover the active molecule itself. Formulation and method-of-use patents can remain commercially significant after composition patents expire, but their ability to block a generic depends on the generic label and product design.
Are there biosimilar risks for neratinib?
No conventional biosimilar pathway applies to neratinib. Neratinib is a chemically synthesized small molecule, not a biologic. Follow-on competitors would generally use the ANDA pathway for a therapeutically equivalent generic, not the biologics license application pathway under section 351(k).
The competitive risk is therefore generic, not biosimilar:
- An ANDA applicant can rely on FDA findings for Nerlynx.
- The applicant must address listed patents through Paragraph IV, section viii, or later certification.
- Therapeutic equivalence and pharmaceutical equivalence will be evaluated under small-molecule requirements.
- A competing branded product could seek approval through a full NDA or another applicable pathway.
What formulation patents protect Nerlynx?
RE43,431 is principally a compound patent. The claims supplied do not expressly recite:
- Tablets;
- Excipients;
- Dissolution profiles;
- Particle-size distributions;
- Release characteristics;
- Specific manufacturing steps;
- A defined treatment regimen.
Any formulation or dosage protection must therefore come from separate patent families. A generic product that uses the same active ingredient but a different formulation could still infringe a formulation patent if it practices all limitations of that patent. Conversely, avoiding a formulation patent would not avoid a live composition claim covering neratinib itself.
How strong is the RE43431 patent estate?
The estate is strongest against products containing the claimed neratinib molecule or its maleate salt while a valid, unexpired composition claim remains enforceable.
| Factor |
Assessment |
| Commercial product match |
Strong; claim 8 identifies neratinib and claim 11 identifies the maleate salt |
| Breadth |
Moderate to broad; claim 1 covers a defined genus |
| Salt coverage |
Strong for listed acid salts, especially maleate |
| Stereochemical coverage |
Strong; both S and R forms are expressly claimed |
| Formulation coverage in supplied claims |
Limited |
| Method-of-use coverage in supplied claims |
None |
| Generic design-around potential |
Limited for the same active molecule; greater for different salt or formulation where later claims permit |
| Dependence on patent term |
High |
| Dependence on later patents |
High for post-core-patent launch analysis |
The strongest litigation position would usually rely on a valid claim directly covering neratinib or neratinib maleate. A genus claim such as claim 1 may provide additional leverage, but its validity analysis is more fact-sensitive.
What generic launch scenarios exist for neratinib?
Launch after core composition expiration
This is the lowest-risk scenario if no later unexpired Orange Book patent covers the active ingredient, salt, formulation, or proposed label.
Paragraph IV launch
A generic applicant could challenge listed patents before expiration. The commercial launch date would depend on litigation, settlement terms, FDA approval timing, and any 180-day first-filer exclusivity.
Section viii carve-out
A generic applicant could omit a patented use from its label, but this approach does not solve a direct composition or salt claim.
Alternative salt or formulation
A different salt or dosage form could reduce exposure to claim 11 or formulation claims. It would not necessarily avoid claim 8, claim 9, or a broader claim 1.
At-risk launch
A company could launch after receiving FDA approval but before final resolution of patent litigation. This exposes the company to damages, possible injunction risk, and enhanced damages if infringement is found.
What litigation and settlement issues matter?
For RE43,431, the key questions are:
- Whether the patent remains enforceable for the proposed launch date.
- Whether the patent is listed for the current Nerlynx reference product.
- Whether the generic product contains neratinib in a claimed form.
- Whether a Paragraph IV suit was filed within the statutory period.
- Whether a settlement includes a licensed entry date.
- Whether the settlement includes acceleration, no-challenge, supply, or authorized-generic provisions.
- Whether later patents are asserted independently of RE43,431.
A settlement involving one patent family does not necessarily clear the full Nerlynx estate. Generic entry may remain blocked by later composition, formulation, method-of-use, or manufacturing patents.
What is the geographic scope of RE43431?
RE43,431 is a United States patent. Its enforceability is limited to U.S. activities covered by 35 U.S.C. §§271 and related provisions.
The international patent estate must be analyzed separately. Comparable patent families may exist in:
- Europe;
- Canada;
- Japan;
- Australia;
- China;
- South Korea;
- Other markets where neratinib was commercialized or protected.
A U.S. patent expiration date does not establish freedom to operate in Europe or other jurisdictions. Patent-term calculations, prosecution history, supplementary protection certificates, opposition proceedings, and local claim construction can differ materially.
Key Takeaways
- RE43,431 covers a quinazoline compound genus that includes neratinib.
- Claim 8 specifically covers the S-enantiomer of neratinib.
- Claim 11 specifically covers neratinib maleate, the marketed Nerlynx form.
- The patent is a reissue and does not receive a new 20-year term from its reissue date.
- The original patent term, patent-term adjustment, pediatric extension, and later continuation patents control launch timing.
- The supplied claims are primarily composition claims, not formulation or method-of-use claims.
- Neratinib faces generic rather than biosimilar competition.
- A Paragraph IV strategy would need to address both the core molecule and later Orange Book-listed patents.
- An alternative salt or formulation may reduce exposure to individual claims but would not automatically avoid broader compound coverage.
- The complete commercial barrier is the combined Nerlynx estate, not RE43,431 in isolation.
FAQs About US RE43431 and Neratinib
Does RE43431 claim Nerlynx tablets?
No. The supplied claims primarily cover neratinib compounds and salts. Tablet composition, excipients, dissolution, and manufacturing protections would require separate claims in other patents.
Does claim 12 cover the marketed form of neratinib?
No. Claim 12 covers the R-enantiomer. The marketed neratinib compound is the S-enantiomer identified in claim 8.
Can a generic avoid claim 11 by using neratinib free base?
Possibly, but not automatically. Claim 8 covers the S-enantiomer without limiting the compound to maleate. A free-base product could still implicate claim 8 or broader claims.
Is neratinib eligible for a biosimilar application?
No. Neratinib is a small-molecule chemical drug. A competing generic would ordinarily proceed through an ANDA rather than a section 351(k) biosimilar application.
Does expiration of RE43431 guarantee immediate generic entry?
No. Later Orange Book-listed patents, pediatric exclusivity, regulatory exclusivity, litigation settlements, formulation patents, and method-of-use claims can affect the actual launch date.
References
-
U.S. Food and Drug Administration. (2017). Nerlynx (neratinib) prescribing information. FDA.
-
United States Patent and Trademark Office. (2013). U.S. Patent No. RE43,431: Quinazoline derivatives. USPTO Patent Center.
-
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book. FDA.
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Federal Food, Drug, and Cosmetic Act, 21 U.S.C. §355(j).
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35 U.S.C. §§154, 156, 251, and 271.
